MySQL基础七：自定义函数

本篇文章参考：http://www.imooc.com/video/2798

不带参数的函数；

mysql> #创建函数；
mysql> SELECT NOW();
+---------------------+
| NOW()               |
+---------------------+
| 2016-04-13 21:53:16 |
+---------------------+
1 row in set (0.00 sec)

mysql> SELECT DATE_FORMAT(NOW(),'%Y年%M月%D日%H点:%I分:%S秒');
+-------------------------------------------------+
| DATE_FORMAT(NOW(),'%Y年%M月%D日%H点:%I分:%S秒') |
+-------------------------------------------------+
| 2016年April月13th日21点:09分:50秒               |
+-------------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT DATE_FORMAT(NOW(),'%Y年%m月%d日-%H点:%I分:%S秒');
+--------------------------------------------------+
| DATE_FORMAT(NOW(),'%Y年%m月%d日-%H点:%I分:%S秒') |
+--------------------------------------------------+
| 2016年04月13日-21点:09分:34秒                    |
+--------------------------------------------------+
1 row in set (0.00 sec)

mysql> #将上述过程封装成函数；
mysql> CREATE FUNCTION f1() RETURNS VARCHAR(30)
    -> RETURN DATE_FORMAT(NOW(),'%Y年%m月%d日-%H点:%I分:%S秒');
Query OK, 0 rows affected (0.03 sec)

mysql> SELECT f1();
+-------------------------------+
| f1()                          |
+-------------------------------+
| 2016年04月13日-22点:10分:29秒 |
+-------------------------------+
1 row in set (0.04 sec)

带参数函数：

mysql> #求两个数的平均值；
mysql>                                                                 
mysql> CREATE FUNCTION f2(num1 SMALLINT UNSIGNED,num2 SMALLINT UNSIGNED)
    -> RETURNS FLOAT(10,2) UNSIGNED
    -> RETURN (num1+num2)/2;
Query OK, 0 rows affected (0.02 sec)

mysql> SELECT f2(15,13);
+-----------+
| f2(15,13) |
+-----------+
|     14.00 |
+-----------+
1 row in set (0.00 sec)

带多个参数的：

mysql> SHOW TABLES;
+------------------+
| Tables_in_world  |
+------------------+
| city             |
| country          |
| countrylanguage  |
| provinces        |
| tdb_goods        |
| tdb_goods_brands |
| tdb_goods_cate   |
| tdb_goods_types  |
| test             |
| users            |
+------------------+
10 rows in set (0.00 sec)

mysql> DESC test;
+----------+---------------------+------+-----+---------+----------------+
| Field    | Type                | Null | Key | Default | Extra          |
+----------+---------------------+------+-----+---------+----------------+
| id       | tinyint(3) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)         | YES  |     | NULL    |                |
+----------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM test;
+----+----------+
| id | username |
+----+----------+
|  1 | John     |
|  2 | 111      |
|  3 | tom%     |
|  4 | NULL     |
|  5 | AA       |
|  6 | BB       |
+----+----------+
6 rows in set (0.00 sec)

mysql> #修改结束符为;-->//
mysql> DELIMITER //
mysql> SELECT VERSION()//
+------------+
| VERSION()  |
+------------+
| 5.7.10-log |
+------------+
1 row in set (0.00 sec)

mysql> #多条语句必须加BEGIN 和END；
mysql> CREATE FUNCTION adduser(username VARCHAR(20))
    -> RETURNS INT UNSIGNED
    -> BEGIN
    -> INSERT test(username) VALUES(username);
    -> RETURN LAST_INSERT_ID();
    -> END
    -> //
Query OK, 0 rows affected (0.02 sec)

mysql> SELECT adduser('Rose')//
+-----------------+
| adduser('Rose') |
+-----------------+
|               7 |
+-----------------+
1 row in set (0.06 sec)

mysql> DELIMITER ;

mysql> SELECT * FROM test;
+----+----------+
| id | username |
+----+----------+
|  1 | John     |
|  2 | 111      |
|  3 | tom%     |
|  4 | NULL     |
|  5 | AA       |
|  6 | BB       |
|  7 | Rose     |
+----+----------+
7 rows in set (0.00 sec)

mysql> #删除函数；
mysql> DROP FUNCTION f1;
Query OK, 0 rows affected (0.01 sec)

mysql> DROP FUNCTION f2;
Query OK, 0 rows affected (0.00 sec)